U.S. patent application number 09/783409 was filed with the patent office on 2001-07-26 for high surface area insulating films.
Invention is credited to Anderson, Barry Jay, Cooper, John Thomas.
Application Number | 20010009173 09/783409 |
Document ID | / |
Family ID | 23315074 |
Filed Date | 2001-07-26 |
United States Patent
Application |
20010009173 |
Kind Code |
A1 |
Cooper, John Thomas ; et
al. |
July 26, 2001 |
High surface area insulating films
Abstract
The present invention provides a high surface area insulating
film comprising a sheet of material, wherein the sheet material
includes a first region and a second region being comprised of the
same material composition. The first region undergoes a
substantially molecular-level deformation and the second region
initially undergoes a substantially geometric deformation when the
sheet material is subjected to an applied elongation along at least
one axis. The first region and the second region are visually
distinct from one another, wherein the second region includes a
plurality of raised rib-like elements and the first region is
substantially free of rib-like elements.
Inventors: |
Cooper, John Thomas; (West
Chester, OH) ; Anderson, Barry Jay; (Cincinnati,
OH) |
Correspondence
Address: |
Stephen T. Murphy
The Procter & Gamble Company
Winton Hill Technical Center
6100 Center Hill Avenue
Cincinnati
OH
45224
US
|
Family ID: |
23315074 |
Appl. No.: |
09/783409 |
Filed: |
February 14, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09783409 |
Feb 14, 2001 |
|
|
|
09336215 |
Jun 18, 1999 |
|
|
|
Current U.S.
Class: |
156/210 |
Current CPC
Class: |
B29D 7/01 20130101; B65D
81/3888 20130101; Y10T 156/1025 20150115; B29C 55/18 20130101 |
Class at
Publication: |
156/210 |
International
Class: |
B32B 031/16 |
Claims
What is claimed is:
1. A high surface area insulating film comprising a sheet of
material, wherein said sheet material includes a first region and a
second region being comprised of the same material composition,
said first region undergoing a substantially molecular-level
deformation and said second region initially undergoing a
substantially geometric deformation when said sheet material is
subjected to an applied elongation along at least one axis, wherein
said first region and said second region are visually distinct from
one another, wherein said second region includes a plurality of
raised rib-like elements and said first region is substantially
free of said rib-like elements.
2. The insulating film of claim 1, wherein said rib-like elements
have a major axis and a minor axis.
3. The insulating film of claim 1, wherein said sheet material
includes a plurality of first regions and a plurality of second
regions comprised of the same material composition, a portion of
said first regions extending in a first direction while the
remainder of said first regions extend in a direction perpendicular
to said first direction to intersect one another, said first
regions forming a boundary completely surrounding said second
regions.
4. A method of insulating an item, said method comprising the steps
of: (a) providing high surface area insulating film comprising a
sheet of material, wherein said sheet material includes a first
region and a second region being comprised of the same material
composition, said first region undergoing a substantially
molecular-level deformation and said second region initially
undergoing a substantially geometric deformation when said sheet
material is subjected to an applied elongation along at least one
axis, wherein said first region and said second region are visually
distinct from one another, wherein said second region includes a
plurality of raised rib-like elements and said first region is
substantially free of said rib-like elements; (b) securing said
sheet material to said article.
5. The method of claim 4, wherein said sheet material is secured to
said article such that said rib-like elements face outwardly from
said article to form trapped air spaces.
6. The method of claim 4, wherein said article is a surface of a
structure, such that said insulating film also provides an air
infiltration barrier.
7. The method of claim 6, wherein said structure is a house.
8. The method of claim 4, wherein said article is an agricultural
product.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to flexible films of the type
commonly utilized for the protection and preservation of various
items and materials by isolation from their environment.
BACKGROUND OF THE INVENTION
[0002] Flexible films, particularly those made of comparatively
inexpensive polymeric materials, have been widely employed for the
protection and preservation of various items and materials.
[0003] As utilized herein, the term "flexible" is utilized to refer
to materials which are capable of being flexed or bent, especially
repeatedly, such that they are pliant and yieldable in response to
externally applied forces. Accordingly, "flexible" is substantially
opposite in meaning to the terms inflexible, rigid, or unyielding.
Materials and structures which are flexible, therefore, may be
altered in shape and structure to accommodate external forces and
to conform to the shape of objects brought into contact with them
without losing their integrity. Flexible films of the type commonly
available are typically formed from materials having consistent
physical properties throughout the film structure, such as stretch,
tensile, and/or elongation properties.
[0004] Film materials such as those described above have been
utilized as an air infiltration barrier in the construction of
exterior walls in buildings such as houses. One commonly utilized
material for such applications is TYVEK.RTM., a spunbonded nonwoven
material manufactured by E. I. DuPont de Nemours. Other exemplary
uses for films to protect items and materials include agricultural
films for weed control around desirable plants and for protection
from low temperatures and frost conditions.
[0005] While such films have been found useful for such
applications, the generally planar nature of most films, coupled
with their thermal conductivity, typically results in a high degree
of surface contact between the protected item and the film and a
corresponding high degree of heat loss or heat gain for the
protected item. Moreover, such films typically exhibit a fairly low
level of elasticity, such that they are prone to pucker and bunch
when wrapped or laid over uneven surfaces.
[0006] Accordingly, it would be desirable to provide a flexible
film which readily conforms to irregular surfaces and reduces heat
loss.
SUMMARY OF THE INVENTION
[0007] The present invention provides a high surface area
insulating film comprising a sheet of material, wherein the sheet
material includes a first region and a second region being
comprised of the same material composition. The first region
undergoes a substantially molecular-level deformation and the
second region initially undergoes a substantially geometric
deformation when the sheet material is subjected to an applied
elongation along at least one axis. The first region and the second
region are visually distinct from one another, wherein the second
region includes a plurality of raised rib-like elements and the
first region is substantially free of rib-like elements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] While the specification concludes with claims particularly
pointing out and distinctly claiming the present invention, it is
believed that the present invention will be better understood from
the following description in conjunction with the accompanying
Drawing Figures, in which like reference numerals identify like
elements, and wherein:
[0009] FIG. 1 is a plan view of a representative insulating film in
accordance with the present invention;
[0010] FIG. 2A is a segmented, perspective illustration of the
polymeric film material of the insulating films of the present
invention in a substantially untensioned condition;
[0011] FIG. 2B is a segmented, perspective illustration of the
polymeric film material of the insulating films of the present
invention in a partially-tensioned condition;
[0012] FIG. 2C is a segmented, perspective illustration of the
polymeric film material of the insulating films of the present
invention in a greater-tensioned condition;
[0013] FIG. 3 is a plan view illustration of another embodiment of
a sheet material useful in the present invention; and
[0014] FIG. 4 is a plan view illustration of a polymeric web
material of FIG. 3 in a partially-tensioned condition similar to
the depiction of FIG. 2B.
DETAILED DESCRIPTION OF THE INVENTION
[0015] FIG. 1 illustrates a representative air infiltration barrier
or agricultural or insulating film material 10 in accordance with
the present invention. FIG. 1 shows a plurality of regions
extending across the material surface. Regions 40 comprise rows of
deeply-embossed deformations in the insulating film material, while
regions 50 comprise intervening undeformed regions. As shown in
FIG. 1, the undeformed regions have axes which extend across the
material
[0016] Additionally, while it is presently preferred to construct
substantially the entire insulating film sheet from a sheet
material having the structure and characteristics of the present
invention, it may be desirable under certain circumstances to
provide such materials in only one or more portions or zones of the
sheet rather than its entirety. For example, a band of such
material having the desired stretch orientation could be provided
in each region of the sheet to provide more localized
properties.
REPRESENTATIVE MATERIALS
[0017] To better illustrate the structural features and performance
advantages of the present invention, FIG. 2A provides a
greatly-enlarged partial perspective view of a segment of sheet
material 52 suitable for use as an air infiltration barrier or
agricultural or insulating film according to the present invention.
Materials such as those illustrated and described herein as
suitable for use in accordance with the present invention, as well
as methods for making and characterizing same, are described in
greater detail in commonly-assigned U.S. Pat. No. 5,518,801, issued
to Chappell, et al. on May 21, 1996, the disclosure of which is
hereby incorporated herein by reference.
[0018] Referring now to FIG. 2A, sheet material 52 includes a
"strainable network" of distinct regions. As used herein, the term
"strainable network" refers to an interconnected and interrelated
group of regions which are able to be extended to some useful
degree in a predetermined direction providing the sheet material
with an elastic-like behavior in response to an applied and
subsequently released elongation. The strainable network includes
at least a first region 64 and a second region 66. Sheet material
52 includes a transitional region 65 which is at the interface
between the first region 64 and the second region 66. The
transitional region 65 will exhibit complex combinations of the
behavior of both the first region and the second region. It is
recognized that every embodiment of such sheet materials suitable
for use in accordance with the present invention will have a
transitional region; however, such materials are defined by the
behavior of the sheet material in the first region 64 and the
second region 66. Therefore, the ensuing description will be
concerned with the behavior of the sheet material in the first
regions and the second regions only since it is not dependent upon
the complex behavior of the sheet material in the transitional
regions 65.
[0019] Sheet material 52 has a first surface 52a and an opposing
second surface 52b. In the preferred embodiment shown in FIG. 2A,
the strainable network includes a plurality of first regions 64 and
a plurality of second regions 66. The first regions 64 have a first
axis 68 and a second axis 69, wherein the first axis 68 is
preferably longer than the second axis 69. The first axis 68 of the
first region 64 is substantially parallel to the longitudinal axis
"L" of the sheet material 52 while the second axis 69 is
substantially parallel to the transverse axis "T" of the sheet
material 52. Preferably, the second axis of the first region, the
width of the first region, is from about 0.01 inches to about 0.5
inches, and more preferably from about 0.03 inches to about 0.25
inches. The second regions 66 have a first axis 70 and a second
axis 71. The first axis 70 is substantially parallel to the
longitudinal axis of the sheet material 52, while the second axis
71 is substantially parallel to the transverse axis of the sheet
material 52. Preferably, the second axis of the second region, the
width of the second region, is from about 0.01 inches to about 2.0
inches, and more preferably from about 0.125 inches to about 1.0
inches. In the preferred embodiment of FIG. 2A, the first regions
64 and the second regions 66 are substantially linear, extending
continuously in a direction substantially parallel to the
longitudinal axis of the sheet material 52.
[0020] The first region 64 has an elastic modulus E1 and a
cross-sectional area A1. The second region 66 has a modulus E2 and
a cross-sectional area A2.
[0021] In the illustrated embodiment, the sheet material 52 has
been "formed" such that the sheet material 52 exhibits a resistive
force along an axis, which in the case of the illustrated
embodiment is substantially parallel to the longitudinal axis of
the web, when subjected to an applied axial elongation in a
direction substantially parallel to the longitudinal axis. As used
herein, the term "formed" refers to the creation of a desired
structure or geometry upon a sheet material that will substantially
retain the desired structure or geometry when it is not subjected
to any externally applied elongations or forces. A sheet material
of the present invention is comprised of at least a first region
and a second region, wherein the first region is visually distinct
from the second region. As used herein, the term "visually
distinct" refers to features of the sheet material which are
readily discernible to the normal naked eye when the sheet material
or objects embodying the sheet material are subjected to normal
use. As used herein the term "surface-pathlength" refers to a
measurement along the topographic surface of the region in question
in a direction substantially parallel to an axis. The method for
determining the surface-pathlength of the respective regions can be
found in the Test Methods section of the above-referenced and
above-incorporated Chappell et al. patent.
[0022] Methods for forming such sheet materials useful in the
present invention include, but are not limited to, embossing by
mating plates or rolls, thermoforming, high pressure hydraulic
forming, or casting. While the entire portion of the web 52 has
been subjected to a forming operation, the present invention may
also be practiced by subjecting to formation only a portion
thereof, e.g., a portion of the material comprising the bag body
20, as will be described in detail below.
[0023] In the preferred embodiment shown in FIG. 2A, the first
regions 64 are substantially planar. That is, the material within
the first region 64 is in substantially the same condition before
and after the formation step undergone by web 52. The second
regions 66 include a plurality of raised rib-like elements 74. The
rib-like elements may be embossed, debossed or a combination
thereof. The rib-like elements 74 have a first or major axis 76
which is substantially parallel to the transverse axis of the web
52 and a second or minor axis 77 which is substantially parallel to
the longitudinal axis of the web 52. The length parallel to the
first axis 76 of the rib-like elements 74 is at least equal to, and
preferably longer than the length parallel to the second axis 77.
Preferably, the ratio of the first axis 76 to the second axis 77 is
at least about 1:1 or greater, and more preferably at least about
2:1 or greater.
[0024] The rib-like elements 74 in the second region 66 may be
separated from one another by unformed areas. Preferably, the
rib-like elements 74 are adjacent one another and are separated by
an unformed area of less than 0.10 inches as measured perpendicular
to the major axis 76 of the rib-like elements 74, and more
preferably, the rib-like elements 74 are contiguous having
essentially no unformed areas between them.
[0025] The first region 64 and the second region 66 each have a
"projected pathlength". As used herein the term "projected
pathlength" refers to the length of a shadow of a region that would
be thrown by parallel light. The projected pathlength of the first
region 64 and the projected pathlength of the second region 66 are
equal to one another.
[0026] The first region 64 has a surface-pathlength, L1, less than
the surface-pathlength, L2, of the second region 66 as measured
topographically in a direction parallel to the longitudinal axis of
the web 52 while the web is in an untensioned condition.
Preferably, the surface-pathlength of the second region 66 is at
least about 15% greater than that of the first region 64, more
preferably at least about 30% greater than that of the first
region, and most preferably at least about 70% greater than that of
the first region. In general, the greater the surface-pathlength of
the second region, the greater will be the elongation of the web
before encountering the force wall. Suitable techniques for
measuring the surface-pathlength of such materials are described in
the above-referenced and above-incorporated Chappell et al.
patent.
[0027] Sheet material 52 exhibits a modified "Poisson lateral
contraction effect" substantially less than that of an otherwise
identical base web of similar material composition. The method for
determining the Poisson lateral contraction effect of a material
can be found in the Test Methods section of the above-referenced
and above-incorporated Chappell et al. patent. Preferably, the
Poisson lateral contraction effect of webs suitable for use in the
present invention is less than about 0.4 when the web is subjected
to about 20% elongation. Preferably, the webs exhibit a Poisson
lateral contraction effect less than about 0.4 when the web is
subjected to about 40, 50 or even 60% elongation. More preferably,
the Poisson lateral contraction effect is less than about 0.3 when
the web is subjected to 20, 40, 50 or 60% elongation. The Poisson
lateral contraction effect of such webs is determined by the amount
of the web material which is occupied by the first and second
regions, respectively. As the area of the sheet material occupied
by the first region increases the Poisson lateral contraction
effect also increases. Conversely, as the area of the sheet
material occupied by the second region increases the Poisson
lateral contraction effect decreases. Preferably, the percent area
of the sheet material occupied by the first area is from about 2%
to about 90%, and more preferably from about 5% to about 50%.
[0028] Sheet materials of the prior art which have at least one
layer of an elastomeric material will generally have a large
Poisson lateral contraction effect, i.e., they will "neck down" as
they elongate in response to an applied force. Web materials useful
in accordance with the present invention can be designed to
moderate if not substantially eliminate the Poisson lateral
contraction effect.
[0029] For sheet material 52, the direction of applied axial
elongation, D, indicated by arrows 80 in FIG. 2A, is substantially
perpendicular to the first axis 76 of the rib-like elements 74. The
rib-like elements 74 are able to unbend or geometrically deform in
a direction substantially perpendicular to their first axis 76 to
allow extension in web 52.
[0030] Referring now to FIG. 2B, as web of sheet material 52 is
subjected to an applied axial elongation, D, indicated by arrows 80
in FIG. 2B, the first region 64 having the shorter
surface-pathlength, L1, provides most of the initial resistive
force, P1, as a result of molecular-level deformation, to the
applied elongation. In this stage, the rib-like elements 74 in the
second region 66 are experiencing geometric deformation, or
unbending and offer minimal resistance to the applied elongation.
In transition to the next stage, the rib-like elements 74 are
becoming aligned with (i.e., coplanar with) the applied elongation.
That is, the second region is exhibiting a change from geometric
deformation to molecular-level deformation. This is the onset of
the force wall. In the stage seen in FIG. 2C, the rib-like elements
74 in the second region 66 have become substantially aligned with
(i.e., coplanar with) the plane of applied elongation (i.e. the
second region has reached its limit of geometric deformation) and
begin to resist further elongation via molecular-level deformation.
The second region 66 now contributes, as a result of
molecular-level deformation, a second resistive force, P2, to
further applied elongation. The resistive forces to elongation
provided by both the molecular-level deformation of the first
region 64 and the molecular-level deformation of the second region
66 provide a total resistive force, PT, which is greater than the
resistive force which is provided by the molecular-level
deformation of the first region 64 and the geometric deformation of
the second region 66.
[0031] The resistive force P1 is substantially greater than the
resistive force P2 when (L1+D) is less than L2. When (L1+D) is less
than L2 the first region provides the initial resistive force P1,
generally satisfying the equation: 1 P1 = ( A1 .times. E1 .times. D
) L1
[0032] When (L1+D) is greater than L2 the first and second regions
provide a combined total resistive force PT to the applied
elongation, D, generally satisfying the equation: 2 PT = ( A1
.times. E1 .times. D ) L1 + ( A2 .times. E2 .times. L1 + D - L2 )
L2
[0033] The maximum elongation occurring while in the stage
corresponding to FIGS. 2A and 2B, before reaching the stage
depicted in FIG. 2C, is the "available stretch" of the formed web
material. The available stretch corresponds to the distance over
which the second region experiences geometric deformation. The
range of available stretch can be varied from about 10% to 100% or
more, and can be largely controlled by the extent to which the
surface-pathlength L2 in the second region exceeds the
surface-pathlength L1 in the first region and the composition of
the base film. The term available stretch is not intended to imply
a limit to the elongation which the web of the present invention
may be subjected to as there are applications where elongation
beyond the available stretch is desirable.
[0034] When the sheet material is subjected to an applied
elongation, the sheet material exhibits an elastic-like behavior as
it extends in the direction of applied elongation and returns to
its substantially untensioned condition once the applied elongation
is removed, unless the sheet material is extended beyond the point
of yielding. The sheet material is able to undergo multiple cycles
of applied elongation without losing its ability to substantially
recover. Accordingly, the web is able to return to its
substantially untensioned condition once the applied elongation is
removed.
[0035] While the sheet material may be easily and reversibly
extended in the direction of applied axial elongation, in a
direction substantially perpendicular to the first axis of the
rib-like elements, the web material is not as easily extended in a
direction substantially parallel to the first axis of the rib-like
elements. The formation of the rib-like elements allows the
rib-like elements to geometrically deform in a direction
substantially perpendicular to the first or major axis of the
rib-like elements, while requiring substantially molecular-level
deformation to extend in a direction substantially parallel to the
first axis of the rib-like elements.
[0036] The amount of applied force required to extend the web is
dependent upon the composition and cross-sectional area of the
sheet material and the width and spacing of the first regions, with
narrower and more widely spaced first regions requiring lower
applied extensional forces to achieve the desired elongation for a
given composition and cross-sectional area. The first axis, (i.e.,
the length) of the first regions is preferably greater than the
second axis, (i.e., the width) of the first regions with a
preferred length to width ratio of from about 5:1 or greater.
[0037] The depth and frequency of rib-like elements can also be
varied to control the available stretch of a web of sheet material
suitable for use in accordance with the present invention. The
available stretch is increased if for a given frequency of rib-like
elements, the height or degree of formation imparted on the
rib-like elements is increased. Similarly, the available stretch is
increased if for a given height or degree of formation, the
frequency of the rib-like elements is increased.
[0038] There are several functional properties that can be
controlled through the application of such materials to insulating
films of the present invention. The functional properties are the
resistive force exerted by the sheet material against an applied
elongation and the available stretch of the sheet material before
the force wall is encountered. The resistive force that is exerted
by the sheet material against an applied elongation is a function
of the material (e.g., composition, molecular structure and
orientation, etc.) and cross-sectional area and the percent of the
projected surface area of the sheet material that is occupied by
the first region. The higher the percent area coverage of the sheet
material by the first region, the higher the resistive force that
the web will exert against an applied elongation for a given
material composition and cross-sectional area. The percent coverage
of the sheet material by the first region is determined in part, if
not wholly, by the widths of the first regions and the spacing
between adjacent first regions.
[0039] The available stretch of the web material is determined by
the surface-pathlength of the second region. The surface-pathlength
of the second region is determined at least in part by the rib-like
element spacing, rib-like element frequency and depth of formation
of the rib-like elements as measured perpendicular to the plane of
the web material. In general, the greater the surface-pathlength of
the second region the greater the available stretch of the web
material.
[0040] As discussed above with regard to FIGS. 2A-2C, the sheet
material 52 initially exhibits a certain resistance to elongation
provided by the first region 64 while the rib-like elements 74 of
the second region 66 undergo geometric motion. As the rib-like
elements transition into the plane of the first regions of the
material, an increased resistance to elongation is exhibited as the
entire sheet material then undergoes molecular-level deformation.
Accordingly, sheet materials of the type depicted in FIGS. 2A-2C
and described in the above-referenced and above-incorporated
Chappell et al. patent provide the performance advantages of the
present invention when formed into air infiltration barriers or
agricultural or insulating films of the present invention.
[0041] An additional benefit realized by the utilization of the
aforementioned sheet materials in constructing insulating films
according to the present invention is the increase in visual and
tactile appeal of such materials. Polymeric films commonly utilized
to form such insulating films are typically comparatively thin in
nature and frequently have a smooth, shiny surface finish. While
some manufacturers utilize a small degree of embossing or other
texturing of the film surface, insulating films made of such
materials still tend to exhibit a slippery and flimsy tactile
impression. Thin materials coupled with substantially
two-dimensional surface geometry also tend to leave the consumer
with an exaggerated impression of the thinness, and perceived lack
of durability, of such insulating films.
[0042] In contrast, sheet materials useful in accordance with the
present invention such as those depicted in FIGS. 2A-2C exhibit a
three-dimensional cross-sectional profile wherein the sheet
material is (in an un-tensioned condition) deformed out of the
predominant plane of the sheet material. This provides additional
surface area for gripping and dissipates the glare normally
associated with substantially planar, smooth surfaces. The
three-dimensional rib-like elements also provide a "cushiony"
tactile impression when the bag is gripped in one's hand, also
contributing to a desirable tactile impression versus conventional
bag materials and providing an enhanced perception of thickness and
durability. The additional texture also reduces noise associated
with certain types of film materials, leading to an enhanced aural
impression.
[0043] Suitable mechanical methods of forming the base material
into a web of sheet material suitable for use in the present
invention are well known in the art and are disclosed in the
aforementioned Chappell et al. patent and commonly-assigned U.S.
Pat. No. 5,650,214, issued Jul. 22, 1997 in the names of Anderson
et al., the disclosures of which are hereby incorporated herein by
reference.
[0044] Another method of forming the base material into a web of
sheet material suitable for use in the present invention is vacuum
forming. An example of a vacuum forming method is disclosed in
commonly assigned U.S. Pat. No. 4,342,314, issued to Radel et al.
on Aug. 3, 1982. Alternatively, the formed web of sheet material
may be hydraulically formed in accordance with the teachings of
commonly assigned U.S. Pat. No. 4,609,518 issued to Curro et al. on
Sep. 2, 1986. The disclosures of each of the above patents are
hereby incorporated herein by reference.
[0045] The method of formation can be accomplished in a static
mode, where one discrete portion of a base film is deformed at a
time. Alternatively, the method of formation can be accomplished
using a continuous, dynamic press for intermittently contacting the
moving web and forming the base material into a formed web material
of the present invention. These and other suitable methods for
forming the web material of the present invention are more fully
described in the above-referenced and above-incorporated Chappell
et al. patent.
[0046] Referring now to FIG. 3, other patterns for first and second
regions may also be employed as sheet materials 52 suitable for use
in accordance with the present invention. The sheet material 52 is
shown in FIG. 3 in its substantially untensioned condition. The
sheet material 52 has two centerlines, a longitudinal centerline,
which is also referred to hereinafter as an axis, line, or
direction "L" and a transverse or lateral centerline, which is also
referred to hereinafter as an axis, line, or direction "T". The
transverse centerline "T" is generally perpendicular to the
longitudinal centerline "L". Materials of the type depicted in FIG.
3 are described in greater detail in the aforementioned Anderson et
al. patent.
[0047] As discussed above with regard to FIGS. 2A-2C, sheet
material 52 includes a "strainable network" of distinct regions.
The strainable network includes a plurality of first regions 60 and
a plurality of second regions 66 which are visually distinct from
one another. Sheet material 52 also includes transitional regions
65 which are located at the interface between the first regions 60
and the second regions 66. The transitional regions 65 will exhibit
complex combinations of the behavior of both the first region and
the second region, as discussed above.
[0048] Sheet material 52 has a first surface, (facing the viewer in
FIG. 3), and an opposing second surface (not shown). In the
preferred embodiment shown in FIG. 3, the strainable network
includes a plurality of first regions 60 and a plurality of second
regions 66. A portion of the first regions 60, indicated generally
as 61, are substantially linear and extend in a first direction.
The remaining first regions 0, indicated generally as 62, are
substantially linear and extend in a second direction which is
substantially perpendicular to the first direction. While it is
preferred that the first direction be perpendicular to the second
direction, other angular relationships between the first direction
and the second direction may be suitable so long as the first
regions 61 and 62 intersect one another. Preferably, the angles
between the first and second directions ranges from about
45.degree. to about 135.degree., with 90.degree. being the most
preferred. The intersection of the first regions 61 and 62 forms a
boundary, indicated by phantom line 63 in FIG. 3, which completely
surrounds the second regions 66.
[0049] Preferably, the width 68 of the first regions 60 is from
about 0.01 inches to about 0.5 inches, and more preferably from
about 0.03 inches to about 0.25 inches. However, other width
dimensions for the first regions 60 may be suitable. Because the
first regions 61 and 62 are perpendicular to one another and
equally spaced apart, the second regions have a square shape.
However, other shapes for the second region 66 are suitable and may
be achieved by changing the spacing between the first regions
and/or the alignment of the first regions 61 and 62 with respect to
one another. The second regions 66 have a first axis 70 and a
second axis 71. The first axis 70 is substantially parallel to the
longitudinal axis of the web material 52, while the second axis 71
is substantially parallel to the transverse axis of the web
material 52. The first regions 60 have an elastic modulus E1 and a
cross-sectional area A1. The second regions 66 have an elastic
modulus E2 and a cross-sectional area A2.
[0050] In the embodiment shown in FIG. 3, the first regions 60 are
substantially planar. That is, the material within the first
regions 60 is in substantially the same condition before and after
the formation step undergone by web 52. The second regions 66
include a plurality of raised rib-like elements 74. The rib-like
elements 74 may be embossed, debossed or a combination thereof. The
rib-like elements 74 have a first or major axis 76 which is
substantially parallel to the longitudinal axis of the web 52 and a
second or minor axis 77 which is substantially parallel to the
transverse axis of the web 52.
[0051] The rib-like elements 74 in the second region 66 may be
separated from one another by unformed areas, essentially
unembossed or debossed, or simply formed as spacing areas.
Preferably, the rib-like elements 74 are adjacent one another and
are separated by an unformed area of less than 0.10 inches as
measured perpendicular to the major axis 76 of the rib-like
elements 74, and more preferably, the rib-like elements 74 are
contiguous having essentially no unformed areas between them.
[0052] The first regions 60 and the second regions 66 each have a
"projected pathlength". As used herein the term "projected
pathlength" refers to the length of a shadow of a region that would
be thrown by parallel light. The projected pathlength of the first
region 60 and the projected pathlength of the second region 66 are
equal to one another.
[0053] The first region 60 has a surface-pathlength, L1, less than
the surface-pathlength, L2, of the second region 66 as measured
topographically in a parallel direction while the web is in an
untensioned condition. Preferably, the surface-pathlength of the
second region 66 is at least about 15% greater than that of the
first region 60, more preferably at least about 30% greater than
that of the first region, and most preferably at least about 70%
greater than that of the first region. In general, the greater the
surface-pathlength of the second region, the greater will be the
elongation of the web before encountering the force wall.
[0054] For sheet material 52, the direction of applied axial
elongation, D, indicated by arrows 80 in FIG. 3, is substantially
perpendicular to the first axis 76 of the rib-like elements 74.
This is due to the fact that the rib-like elements 74 are able to
unbend or geometrically deform in a direction substantially
perpendicular to their first axis 76 to allow extension in web
52.
[0055] Referring now to FIG. 4, as web 52 is subjected to an
applied axial elongation, D, indicated by arrows 80 in FIG. 4, the
first regions 60 having the shorter surface-pathlength, L1, provide
most of the initial resistive force, P1, as a result of
molecular-level deformation, to the applied elongation which
corresponds to stage I. While in stage I, the rib-like elements 74
in the second regions 66 are experiencing geometric deformation, or
unbending and offer minimal resistance to the applied elongation.
In addition, the shape of the second regions 66 changes as a result
of the movement of the reticulated structure formed by the
intersecting first regions 61 and 62. Accordingly, as the web 52 is
subjected to the applied elongation, the first regions 61 and 62
experience geometric deformation or bending, thereby changing the
shape of the second regions 66. The second regions are extended or
lengthened in a direction parallel to the direction of applied
elongation, and collapse or shrink in a direction perpendicular to
the direction of applied elongation.
[0056] In addition to the aforementioned elastic-like properties, a
sheet material of the type depicted in FIGS. 3 and 4 is believed to
provide a softer, more cloth-like texture and appearance, and is
more quiet in use.
[0057] Various compositions suitable for constructing the air
infiltration barriers or agricultural or insulating films of the
present invention include substantially impermeable materials such
as polyvinyl chloride (PVC), polyvinylidene chloride (PVDC),
polyethylene (PE), polypropylene (PP), aluminum foil, coated
(waxed, etc.) and uncoated paper, coated nonwovens etc., and
substantially permeable materials such as scrims, meshes, wovens,
nonwovens, or perforated or porous films, whether predominantly
two-dimensional in nature or formed into three-dimensional
structures. Such materials may comprise a single composition or
layer or may be a composite structure of multiple materials.
[0058] While particular embodiments of the present invention have
been illustrated and described, it would be obvious to those
skilled in the art that various other changes and modifications can
be made without departing from the spirit and scope of the
invention. It is therefore intended to cover in the appended claims
all such changes and modifications that are within the scope of
this invention.
* * * * *